21 Sep
2020
21 Sep
'20
4:13 a.m.
On Sun, Sep 20, 2020 at 4:58 PM Doug McIlroy <doug(a)cs.dartmouth.edu> wrote:
To put it more strongly. this is not a legal C source file.
char *s = NULL;
But this is.
char *s = 0;
Hmmm ... Doug - As the risk of playing language lawyer here, I'm going to
argue that between sections 6.3.2.3 and 7.19 the first is legal.
Cut/pasted from my cope of the 2017 standard (I don't think this has
changed in later drafts):
ISO/IEC 9899:2017 Section 6.3.2.3 *Pointers*
*....*
1.
An integer constant expression with the value 0, or such an expression
cast to type void *, is called a null pointer constant.67) If a null
pointer constant is converted to a pointer type, the resulting pointer,
called a null pointer, is guaranteed to compare unequal to a pointer to
any object or function.
2.
67)The macro NULL is defined in <stddef.h> (and other headers) as a null
pointer constant; see 7.19.
3.
....
ISO/IEC 9899:2017 Section 7.19 *Common definitions <stddef,h>*
....
1.
The macros are
NULL
which expands to an implementation-defined null pointer constant;
For whatever its worth, in a number of common coding standards where I have
worked, have always required that when NULL was used, it was always cast
first to the actual data type. Yes, this is verbose, but it means that a
casual reader sees the type and in particularly in a commerical SW
development setting, that is money in the bank from a maintence standpoint
-- IIRC Gimpel's flexelint <https://www.gimpel.com/about.html> (which IMO
oppinion was always the best lint around), has a switch that will force
that behavior.
As I understand it, the idea behind -Wall *et al*, is that if we can get
code to be 'flexelint clean' the number of latent bugs drops dramatically.
This is particularly true when dealing with code that started be written on
a system with one word or pointer size and now needs to run elsewhere;
which is a common issue commerical ISVs live a great deal [this is a
codified in the 10th of Henry's commandments:
Thou shalt foreswear, renounce, and abjure the vile heresy which claimeth
that ``All the world's a VAX'', and have no commerce with the benighted
heathens who cling to this barbarous belief, that the days of thy program
may be long even though the days of thy current machine be short.
: .